1. Field of the Invention
The present invention relates to a muffler applied for smaller engines.
2. Prior Art
Mufflers applied for the smaller engines used in conventional brush cutters or chain saws are constructed such that, as shown in FIG. 1, an exhaust gas first expansion chamber 2 having an exhaust gas inlet 1 connecting to an exhaust gas outlet of the engine (not shown in the figure) and an exhaust gas second expansion chamber 4 having an exhaust gas outlet 3, the first expansion chamber 2 and the second expansion chamber 4 being separated by a partition board, a part of the partition board being removed to install an exhaust gas purifier 5 made of stainless steel and coated with a catalyst to purify the gas passing through the purifier 5. Said purifier is provided with innumerable numbers of honeycomb-like small holes.
Another conventional mufflers are constructed such that, as shown in FIG. 2, the exhaust gas first expansion chamber 2 having the exhaust gas inlet 1 connecting to the exhaust gas outlet of the engine and the exhaust gas second expansion chamber 4 having an exhaust gas outlet 3, an exhaust gas receiver 6 located in the first expansion chamber 2 and one end of the exhaust gas receiver 6 is closed and the other end of which being opened, said exhaust gas receiver 6 being provided with a plurality of through holes 6b and the open end of which being placed facing to the exhaust gas inlet 1 in the first expansion chamber 2 and the first expansion chamber and the second expansion chamber 4 being separated with a partition board, one part of the partition board being removed and an exhaust gas purifier 5 made of stainless steel and coated with a catalyst to purify the exhaust gas passing through the honeycomb small holes is applied.
In conventional engine mufflers shown in FIG. 1, an exhaust gas of the engine is introduced into the first gas expansion chamber 2 through the gas inlet 1, passing through the exhaust gas purifier 5 provided in the chamber and the exhaust gas is introduced into the second expansion chamber 4 and the gas is exhausted to the atmosphere through the exhaust gas outlet 3. Accordingly, an outside wall 2a of the first expansion chamber 2 and an outside wall 4a of the second expansion chamber 4 are heated up to approximately 700xcx9c800xc2x0 C. by the heat of the exhaust gas. When the muffler is installed to the engine it is required to provide a metallic cover plate 7 at a position with a predetermined distance from the outside wall 4a and further it is required to install a heat durable plastic cover plate 8 at a position with another predetermined distance from the metallic cover plate 7. Accordingly, an exterior shape of the muffler becomes larger against a tendency to make the engine assembly smaller.
In the muffler illustrated in FIG. 2, one open end of the exhaust gas receiver 6 provided with a plurality of gas through holes 6b on a cylindrical surface 6a is placed facing to the exhaust gas inlet 1 to increase an efficiency to absorb the sound of the muffler. Incomplete combustion gasses are burnt and generation of unfavorable carbon monoxide or nitrogen oxides is controlled. Even such improvement has been added, since the outside wall 2a of the first expansion chamber 2 and an outside wall 4a of the second expansion chamber 4 are heated by the exhaust gas up to approximately 700xcx9c800xc2x0 C., the metallic cover plate 7 must be added at a location with a predetermined distance from the outside wall 4a of the muffler and further the heat durable plastic cover 8 is required at a location with a predetermined distance from the metallic cover plate 7. The engine assembly including the muffler becomes larger against the tendency to make the engine assembly smaller.
The present invention is to offer an improved engine muffler to keep the outside wall of the second expansion chamber not to become hotter.
The present invention is explained with reference to FIG. 3. A muffler provided with a first expansion chamber 12 of the exhaust gas provided with an exhaust gas inlet 11 connecting to an exhaust gas outlet aperture of the 2 cycle or the 4 cycle engine, a second expansion chamber 14 provided with a gas exhaust outlet 13, the first expansion chamber 12 and the second expansion chamber 14 are separated with a partition board 20, a part of which being cut out to place a first exhaust gas purifier 15 coated with a catalyst to purify the exhaust gas, the purifier 15 is provided with innumerable numbers of small holes. The wall that does not face to the engine of said second expansion chamber 14 is made as a double-wall construction having a wall 14a and a wall 14b with a predetermined distance between them. It is of course possible to have a double wall construction having a wall 12a and a wall 12b as shown in FIG. 4A.
It goes without saying that a catalyst is not applied to the first exhaust gas purifier if there is no particular restriction in the gas purification concentration degree. This case is shown in FIG. 4B.
The muffler is also explained with reference to FIG. 5A that the double walls 12a and 12b, 14a and 14b are packed with a heat insulating material to enhance the heat insulating efficiency.
It goes without saying that a catalyst is not applied to the first exhaust gas purifier if there is no particular restriction in the gas purification concentration degree. This case is shown in FIG. 5B.
The engine muffler is also devised as illustrated with reference to FIG. 6. A cover plate 17 provided with one open aperture at a place surrounding the exhaust gas purifier 15 in the first expansion chamber 12 for the engine of 2 cycle or 4 cycle type illustrated in FIG. 3 and another cover plate 17xe2x80x2 surrounding said gas purifier 15 in the second expansion chamber 14 provided with one open aperture at a place surrounding the exhaust gas purifier 15 in the second expansion room 14 are added. In such a manner, a gas introducing aperture is provided in the first expansion chamber 12 and a gas exhausting aperture is provided in the second expansion chamber 14. Thus, the flow of gas is rectified to store the heat within the cover pate 17 and the cover plate 17xe2x80x2 to prevent the heat from being transferred to the outside walls.
It goes without saying that a production process becomes easier if the partition board 20 and the cover plate 17 located in the first expansion chamber 12 are manufactured in an integral molding manner.
The engine muffler is also illustrated with reference to FIG. 7. Said engine muffler is an improved ones shown in FIG. 3 and FIG. 6. Apart of the double walls 14a and 14b in the second expansion chamber 14 is removed to provide an open aperture 14c through which the exhaust gas is partly released outside. The outside wall 14xe2x80x2 is fastened to a cover plate 19 with a bolt and a nut. Further, a cover plate 17xe2x80x2 for the exhaust gas purifier 15 in the second expansion chamber 14 is fastened to the partition board 20 with a bolt and a nut. If required, the cover plates 14xe2x80x2 and 17xe2x80x2 are unfastened to take out the exhaust gas purifier 15 for replacement or cleaning. This model change is done to assist the life of the exhaust gas purifier 15.
A distance between the cover plate 17 in the first expansion chamber 12 and the exhaust gas purifier 15 is widened. Meanwhile, a distance between the cover plate 17xe2x80x2 in the second expansion chamber 14 and both sides of the exhaust gas purifier 15 is made nil. By this construction it becomes easier to take out the exhaust gas purifier 15 from the second expansion chamber 14. It is also easy to put back the exhaust gas purifier 15 to the place where it is located in the first expansion chamber 12.
The muffler illustrated in FIG. 4A is reconstructed to have the cover plates 17 and 17xe2x80x2 as illustrated in FIG. 8. It is also reconstructed to have the double walls construction such as walls 12a, 12b and 14a, 14b. 
The muffler in FIG. 9 is made to have the double walls 12a, 12b and 14a, 14b and packed with the heat insulating material 16 to improve the heat insulating efficiency much more.
The muffler in FIG. 10 is provided with a second exhaust gas purifier 18 to the muffler shown in FIG. 4A to improve exhaust gas purification efficiency, to eliminate muffler""s sound and to improve the heat insulation efficiency.
The muffler in FIG. 11 is provided with an improved second exhaust gas purifier 18. The purifier 18 is located nearer the exhaust gas inlet 11.
The muffler in FIG. 12 is manufactured to have its closed end of the second exhaust gas purifier 18 welded onto the partition board 20. The heat insulation material 16 is packed between the walls 12a, 12b and 14a, 14b, respectively.
The muffler in FIG. 13 is an improved ones by covering the circumference of the first exhaust gas purifier 15 with the cover plates 17 and 17xe2x80x2 of the muffler shown in FIG. 12.
The muffler in FIG. 14 is packed with the heat insulating material 16 between the walls 12a, 12b and 14a, 14b shown in FIG. 13.